A078568 Repunits concatenated with A000422, where A000422 is the concatenation of numbers from n down to 1.

11, 1121, 111321, 11114321, 1111154321, 111111654321, 11111117654321, 1111111187654321, 111111111987654321, 111111111110987654321, 111111111111110987654321, 111111111111121110987654321

Offset: 1

Author

Jason Earls, Nov 29 2002

Keywords

• base
• nonn

Comments

See A078569 for the primes arising in this sequence.

Links

• Harvey P. Dale, Table of n, a(n) for n = 1..277

Crossrefs

Cf. A002275, A000422, A078569.

Programs

Mathematica

a[n_Integer] := Block[{repUn = Array[Array[1 &, #] &, {n}], nTo1 = Range[ Range@n, 1, -1]}, ToExpression/@ StringJoin/@ Map[ToString, Flatten/@ Thread@{repUn, nTo1}, {2}]]; a[100] (* or *)
a[n_Integer] := FromDigits /@ StringJoin /@ Table[ Join[ PadLeft[{}, i, "1"], ToString /@ Range[i, 1, -1]], {i, n}]; a[100] (* Mikk Heidemaa, May 03 2021 *)
Table[FromDigits[Join[PadRight[{},n,1],Flatten[IntegerDigits/@Range[n,1,-1]]]],{n,20}] (* Harvey P. Dale, Aug 23 2022 *)